Dynamic-absorber for the suppression of suspension vibrations

ABSTRACT

A rotary actuated arm assembly for positioning a tranducer over a data track of a rotating magnetic disk includes an extended load beam having an etched cavity along its top surface and shaped to function as a dynamic absorbing member for absorbing undesirable vibrations and resonances occurring in high speed mechanisms such as disk drives.

This is a division of U.S. patent application Ser. No. 08/998,633,filing date Dec. 29, 1997, U.S. Pat. No. 5,949,617 A Dynamic-AbsorberFor The Suppression Of Suspension Vibtrations, assigned to the sameassignee as the present invention.

BACKGROUND OF THE INVENTION

(1). Technical Field

This invention relates to the field of disk drives, in particular, to amethod for absorbing unwanted vibrations and resonances in dynamicmechanisms, such as disk drives, is fabricated with an integral dynamicabsorber that can be formed where the vibration is to be suppressed. Theabsorbing system is disposed at a predetermined location on a load beamsuspension.

(2). Description of the Prior Art

The following two documents relate to methods dealing with vibrationsuppression of head suspension assemblies.

U.S. Pat. No. 4,932,019 issued Jun. 5, 1990 to A. Bessho describes avibration absorbing member for reducing resonance energy in an opticaldisk drive, but it also is used in conjunction with a drive base and nota head suspension assembly as in the invention.

U.S. Pat. No. 4,703,470 issued Oct. 27, 1987 to Castagna, et al,discloses a dynamic absorber used in a disk drive, but the absorberdescribed has a viscoelastic link element between the absorber base andabsorber mass, and is only described as being used on the drive carriageor base casting.

It is well known that high speed mechanisms having moving parts aresusceptible to damaging vibratory effects which reduce the expected lifeof the mechanism. As an example, disk drives which use actuators andassociated suspensions for bidirectional accessing of data tracks of arotating disk suffer from undesirable vibrations and resonances. In thepast the designer would add visco-elastic dampers to the suspension.However, outgassing would often occur with visco-elastic damperscreating friction polymers on the slider/disk interface thereby causingpremature failure of the disk drive system.

Furthermore, a major objective for improved performance of disk drivesis to achieve reduction in the access time of the rotating disk. Theaccess time is dependent upon the mass of the suspension assembly. Thus,it is desirable to reduce the mass of the suspension assembly. Thereduction of mass, if not correctly accomplished, may in effect increasethe access time due to the increased severity of the structuralresonances of the suspension.

Several methods dealing with vibration absorbing devices have beenemployed in the past to damp unwanted resonance frequencies of dynamicoperating mechanisms. The absorbing devices are designed to undergo aresonance at a predetemined frequency which is related to the undesiredresonance frequency. Such prior art devices are overly sensitive whenundergoing assembly and handling and are not considered reliable sincethey may fail mechanically during operation.

In a hard disk drive, typically a head slider is positioned by a headsuspension assembly (HSA) over a magnetic disk to facilitate reading andwriting of information to the disk. The constituent elements of standardHSAs include a swage plate, a resilient zone, a load beam, a flexure anda head slider. The swage plate is positioned at a proximal end of theload beam, adjacent to the resilient zone and is mounted to thesuspension by means of a boss and by laser welding. The swage plateprovides stiffness to the rear mount section and is configured formounting the load beam to an actuator arm of a disk drive. The flexureis positioned at a distal end of the load beam. Mounted to the flexureis a head slider with a read/write orientation with respect to anassociated disk.

SUMMARY OF THE INVENTION

It is and object of the invention to provide a novel and improveddynamic absorber for reducing unwanted vibrations, resonances, and noisein high speed mechanisms, such as disk drives.

It is another object of the invention is to provide a dynamic absorberthat does not add mass to the disk drive system thereby achievingreduction in the access time of the magnetic heads to selected datatracks of the rotating disk.

It is another object of the invention to provide a dynamic absorber thatdoes not require additional process, material, or assembly. It isessentially free after the initial development and setup.

It is still another object of the invention not to introduce foreignmaterial into the disk drive. It will not outgass, corrode, wear, orfall off the suspension.

The foregoing objects of the invention are accomplished and thedisadvantages of the prior art overcome by the provision of a disk drivecomprising a dynamic absorber that is constitutively included into aload beam of a head suspension assembly. A load beam is typically madeof a sheet of stainless steel. Cavities are often etched out of thesuspension for control of stiffness, mode shape, and for mass-reduction.The dynamic absorber can be etched within the load beam configurationand within the shape of the cavity, which as mentioned previously can bereconfigured to include the shape of a dynamic absorber.

When a suspension is designed, the mode-shape and natural frequenciesare usually known. They are often predicted by simulation and verifiedby experiments. If a particular mode is of special concern, a dynamicaborber can be placed at a location where the vibration is to besuppressed. To suppress vertical deflection, the absorber can be asimple cantilever beam, or a cantilever with an enlarged tip. This typeof absorber is suitable at the antinodes of the vibration, where thevertical displacement is greatest. To suppress rotation, the absorbercan be a T-bar. This type of absorber is suitable at the nodes of thevibration, where the rotation is greatest. The natural frequencies ofthe absorber should match the mode to be suppressed.

Occasionally the natural frequencies of the absorber need to beadjusted, either due to variation of the suspension thickness, or due toa change in the vibration to be suppressed. The adjustment can beaccomplished by creating a cavity at the absorber, for example using alaser beam. The amount of adjustment can be controlled by the locationof the cavity. The natural frequency is increased if the cavity is nearthe free end of the absorber. This novel adjustment scheme overcomes thedisadvantage of several prior arts, which failed to achieve desiredaccuracy in natural frequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective illustration of a typical head suspensionassembly used on disk drives.

FIG. 2 shows a top view of a prior art load beam.

FIG. 3 is a side elevation view of the load beam of FIG. 2.

FIG. 4A shows a single vertical vibration mode of a load beam of theprior art.

FIG. 4B shows a double vertical vibration mode of a load beam of theprior art.

FIG. 4C shows a combination of a vertical and rotational vibration modesof a load beam of the prior art.

FIG. 5 illustrates shapes of various dynamic absorbers, of theinvention, as applied to load beam suspensions.

FIG. 5A illustrates a dynamic absorber, of the invention, for thesuppression of a vertical vibration as applied to a load beamsuspension.

FIG. 5B illustrates a dynamic absorber, of the invention, for thesuppression of a vertical vibration as applied to a load beamsuspension.

FIG. 5C illustrates a combination of dynamic absorbers, of theinvention, for the suppression of a combination of vibrations as appliedto load beam suspensions.

FIG. 5D illustrates a dynamic absorber, of the invention, placed withina location previously occupied by a standard cavity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A head suspension assembly with improved vibration dissipatingcharacteristics is described. With reference to FIG. 1, there is shown aperspective view of a head suspension assembly 9 comprising a slider 21having top, bottom and side surfaces. Along its trailing side surface, atransducer, not shown, is attached so that information can be writtenand read from the rotating magnetic disk 33, over which the sliderflies. Note that the top surface of the slider body is attached to aflexure element 17 which typically comprises a thin piece of metalattached to a load beam 11. Most often both flexure and load beaminclude various shaped slots which increases their combined flexability;this is one way that the slider is given freedom of movement to allowfor the overall height variations present on the surface of the disk.The load beam 11 is shown mounted to the actuator arm via a swage plate12.

During operation of the disk drive, the rotating magnetic disk providesan aerodynamic lift force to the slider 21, while an opposing gram loadforce is applied to the slider through the suspension assembly 9. Theequilibrium of the two opposing forces determines the flying height ofthe slider 21 and its transducer relative to the disk surface 15. Foroptimum operation, the suspension structure will provide a high firstbending mode resonant frequency so that the slider is insensitive to lowfrequency mechanical disturbance caused by spindle vibration, servoaction, and air drag on the suspension, etc.

As the track density of hard disk drives increase, more and moreattention needs to be paid to the design of the load beam suspension,since suspension resonances and in-plane suspension motions limit trackdensity. Refer to FIGS. 4A to 4C showing various vibration modes of atypical load beam suspension, though highly exaggerated. In recentyears, the trend in load beam suspension design has been toward smallersuspensions, and much research and development work must still be donein the areas of load beam design to reduce sway modes and otherundesirable resonances.

Referring now to FIGS. 2 and 3, illustrating, respectively, top and sideviews of a prior art load beam suspension member 11. The load beam 11 ispreferably made in a truncated triangular shape having flanges 71 alongits sides and an extending tongue 72 at its narrow end. The side flangesare formed as L-shaped channels to provide rigidity and stiffness to theload beam section. The tongue 72 has a flexure, not shown, that is laserwelded to the load beam in the area of an alignment cavity 14.

The leaf spring 18 between the L-shaped channel section 71 and the swageplate 12 is formed often with a trapezoidal-like cutout 19 to provideflexability. The flexible, leaf spring section 18 is formed to provide adesired load force that counteracts the aerodynamic lift force generatedby the rotating disk during operation of the disk drive. The load forcecomes from bending the suspension from the phantom position, shown inFIG. 3, to the raised position as indicated by the arrow.

The vibration of the suspension in magnetic recording drives isextremely harmful. It interferes with the servo performance, and mayalso cause slider-disk contact which may lead to catastrophic failure.In the prior art, viscoelastic dampers are often applied to thesuspension. The increased reflected inertia to the servo actuator,because of the added mass, requires a slower operating speed, hencelimiting progression in suspension performance. The viscoelastic dampersalso free leaches materials creating friction polymers on theslider/disk interface and causing premature failure.

The invention takes advantage of the following facts. A load beam istypically fabricated from a sheet of stainless steel. Cavities are oftenetched into the suspension to be used for alignment, stiffness control,and weight reduction.

When a suspension is designed, the mode shape and natural frequenciesare usually known and predicted by simulation and verified byexperiments. If a particular mode shape is of special concern, the keyaspect of the invention is the addition of a dynamic absorber that canbe etched at a location where the vibration is to be suppressed. Somevibration may not coincide with a natural frequency of the head gimbalsassembly, but requires suppression because of their large amplitude. Forexample, the spindle noise and the servo actuator motion may be strongenough to cause concern, even if they do not coincide with one of thesuspension resonant frequencies. FIGS. 5A to 5D illustrate variousshapes of dynamic absorbers, of the invention, that can be incorporatedinto the suspension to counterpoise unwanted vibrations. To suppressvertical deflection, the absorber can be a cantilever with an enlargedtip 41, or 42 or a simple cantilever beam as illustrated in 43, or in44. This type of absorber is suitable at the antinodes of thesuspension. To suppress rotation, the absorber shape would take the formof a torsional bar 45 suspended on a pair of pivot hinges 4, and 5.Dynamic absorbers can be placed in combination to suppress both verticaland rotational vibrations as shown in FIG. 5C, or can be placed anywherealong the length of the suspension including within the standard cavitylocations taken by trapezoidal-like cutout 19 and alignment cavity 14.In the case of a cantilever beam, the natural frequency of the absorberis proportional to the beam thickness, and inversely proportional to thesquare of the beam length, independent of the beam width. However, theuseful band-width of the absorber increases with the width of the beam.As an example, a 50 μm thick absorber for the suppression of 4.5 kHzvibration is approximately 3 mm long. If a low-frequency vibration is tobe absorbed, the simple cantilever beam may be too long to fit into theload beam. In this case, an enlarged tip may be incorporated. With ofwithout an enlarged tip, this type of absorber is suitable at antinodesof the suspension, where the vertical deflection is greatest.

In manufacturing, the incoming load beam thickness may vary. Thus thenatural frequency of an absorber may deviate from desired value.Adjustment may be needed at times. Also in manufacturing, it may bedesirable to modify the specification of a suspension. For example, thefrequency to be suppressed may change due to a change in the designeddisk speed. A novel feature is described herein to facilitate theadjustment and modification. In FIG. 5B, an optional cavity 47 is shownon the cantilever beam 43. When the cavity 47 is located near the tip ofthe cantilever beam, the natural frequency of the absorber increases.When the cavity is located near the base of the cantilever beam, thenatural frequency of the absorber decreases. By the intermediate-valuetheorem of calculus, the natural frequency can be adjusted continuouslywithin a finite range, by selecting the location of the cavity alone,without changing the cavity size. Obviously, the range of adjustmentincreases with the cavity size.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A head suspension assembly having a dynamicabsorbing member for absorbing undesirable vibrations and resonances inhigh speed mechanisms such as disk drives, the head suspension assemblycomprising: an elongated load beam having a shaped aperture etchedthrough its top surface, said shaped aperture having a continuousperimeter, said perimeter including a member that is patterned tovibrate as a secondary spring mass for absorbing said undesirablevibrations and resonances.
 2. The head suspension assembly according toclaim 1 wherein said secondary spring mass has a shape of a simplecantilever beam for suppressing an undesirable vertical high-frequencyvibration.
 3. The head suspension assembly according to claim 1 whereinsaid secondary spring mass has a shape of a cantilever with an enlargedtip for suppressing an undesirable vertical low-frequency vibration. 4.The head suspension assembly according to claim 1 wherein said secondaryspring mass suppresses either a low or high vertical vibration, saidshaped aperture with said secondary spring mass is etched at thevibration antinodes of the load beam.
 5. The head suspension assemblyaccording to claim 1 wherein said secondary spring mass suppresses anundesirable rotational deflection said secondary spring mass has a shapeof a T-bar.
 6. The head suspension assembly according to claim 1 whereinsaid secondary spring mass suppresses an undesirable rotationaldeflection said shaped aperture with said secondary spring mass isetched at the deflection nodes of the load beam.
 7. The head suspensionassembly according to claim 1 wherein said secondary spring mass doesnot add mass to said suspension assembly whereby removing materialenhances the disk drives access time.
 8. The head suspension assemblyaccording to claim 1 wherein said secondary spring mass eliminates needfor additional assembly time as required when adding external damperssuch as viscoelastic or adhesive dampers.